It should be easy enough to just compile Gridwars on a linux machine, to get it to be a linux version. That after all is the whole point of Max being cross-platform. You shouldn't have to make any changes to get it ported.
Problem is now you have to test it on that platform. Just compile and ship isnt an option. You still have to test every function to make sure nothing funny is happening. That's the joy of cross platform development.